CN109585108B

CN109585108B - Method for producing R-T-B sintered magnet and diffusion source

Info

Publication number: CN109585108B
Application number: CN201811140238.9A
Authority: CN
Inventors: 国吉太
Original assignee: Hitachi Metals Ltd
Current assignee: Proterial Ltd
Priority date: 2017-09-28
Filing date: 2018-09-28
Publication date: 2021-05-14
Anticipated expiration: 2038-09-28
Also published as: CN109585108A

Abstract

The method comprises the following steps: a step for preparing a R1-T-B sintered magnet material (R1 is a rare earth element, and T is Fe or Fe and Co); a step of preparing an alloy containing at least one rare earth element R2 that necessarily includes Dy and Tb and occupies 40 mass% or more of the entire alloy; a step of heat-treating the alloy at a temperature not lower than 270 ℃ and not higher than the melting point of the alloy, and pulverizing the heat-treated alloy to obtain a diffusion source; and a diffusion step of disposing the R1-T-B sintered magnet material and the diffusion source in a processing vessel, heating the R1-T-B sintered magnet material and the diffusion source to a temperature not higher than the sintering temperature of the R1-T-B sintered magnet material, and diffusing at least one of Dy and Tb contained in the diffusion source from the surface of the R1-T-B sintered magnet material into the inside, wherein the alloy is an alloy obtained by a melt-spinning method.

Description

Method for producing R-T-B sintered magnet and diffusion source

Technical Field

The present disclosure relates to a method for producing an R-T-B sintered magnet (R is a rare earth element and T is Fe or Fe and Co), and a diffusion source.

Background

With R₂T₁₄An R-T-B sintered magnet having a B-type compound as a main phase is known as the highest performance magnet among permanent magnets, and is used for various engines such as a Voice Coil Motor (VCM) for a hard disk drive, an engine for a hybrid vehicle, and home electric appliances.

Intrinsic coercive force H of R-T-B sintered magnet at high temperature_cJ(hereinafter, it will be simply referred to as "H_cJ") decreases, so irreversible thermal demagnetization occurs. In order to avoid irreversible thermal demagnetization, when used for engines or the like, it is required to maintain high H even at high temperatures_cJ。

Regarding R-T-B sintered magnets, it is known that if R is added₂T₁₄A part of R in the B type compound phase is replaced by heavy rare earth element RH (Dy, Tb), then H_cJAnd (4) improving. In order to obtain a high H at high temperatures_cJAdding a large amount of heavy rare earth to an R-T-B sintered magnetElemental RH is effective. However, in the R-T-B sintered magnet, if the light rare earth element RL (Nd, Pr) as R is replaced with the heavy rare earth element RH, H will be present_cJIncreased but residual magnetic flux density B_r(hereinafter, it will be simply referred to as "B_r") reduced. In addition, since the heavy rare earth element RH is a scarce resource, it is required to reduce the amount thereof.

For this reason, in recent years, studies have been made to avoid B_rReduced mode for increasing H of R-T-B sintered magnet with less heavy rare earth element RH_cJ. For example, the following scheme is proposed: the surface of the sintered magnet is subjected to heat treatment in a state where a fluoride or an oxide of the heavy rare earth element RH, or a metal M or an alloy of M, alone or in combination, is present on the surface of the sintered magnet, whereby the heavy rare earth element RH contributing to improvement of coercive force is diffused into the magnet.

Patent document 1 discloses a method for producing a rare earth magnet, which comprises mixing R¹ ₂T₁₄R with B type compound as main phase¹R-containing component present on surface of-T-B sintered body²And M, and R is caused to be a powder by heat treatment²And diffusing the element from the alloy powder into the sintered body. Wherein R is¹Is one or more elements selected from rare earth elements including Sc and Y, and T is Fe and/or Co. In addition, R²Is one or more elements selected from rare earth elements including Sc and Y, and M is a metal element such as B, C, Al, Si, Ti, etc.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2011-14668

Disclosure of Invention

Problems to be solved by the invention

In the production method disclosed in patent document 1, R is contained as²And M, using a quenched alloy powder. The quenched alloy powder contains R²-a microcrystalline or amorphous alloy having an average particle size of the intermetallic compound phase of 3 μ M or less.

The composition contains Dy andin the method of diffusing at least one of Tb, by diffusing at least one of Dy and Tb more uniformly, magnetic characteristics (H) between individual magnets are realized_cJ) The reduction of the ripple.

Means for solving the problems

The method for producing an R-T-B sintered magnet according to the present disclosure, in an exemplary embodiment, includes: a step for preparing a R1-T-B sintered magnet material (R1 is a rare earth element, and T is Fe or Fe and Co); a step of preparing an alloy containing at least one rare earth element R2 that necessarily includes Dy and Tb and occupies 40 mass% or more of the entire alloy; a step of heat-treating the alloy at a temperature not lower than 270 ℃ and not higher than the melting point of the alloy, and pulverizing the heat-treated alloy to obtain a diffusion source; and a diffusion step of disposing the R1-T-B sintered magnet material and the diffusion source in a process container, heating the R1-T-B sintered magnet material and the diffusion source to a temperature not higher than the sintering temperature of the R1-T-B sintered magnet material, and diffusing at least one of Dy and Tb contained in the diffusion source from the surface of the R1-T-B sintered magnet material into the interior, wherein the alloy is an alloy produced by a melt spinning method (melt spinning).

In another exemplary embodiment, a method for producing an R-T-B sintered magnet according to the present disclosure includes: a step for preparing a R1-T-B sintered magnet material (R1 is a rare earth element, and T is Fe or Fe and Co); a step of crushing an alloy containing at least one rare earth element R2 that necessarily includes Dy and Tb and occupies 40 mass% or more of the entire alloy to prepare an alloy powder; a step of heat-treating the alloy powder at a temperature not lower than 270 ℃ and not higher than the melting point of the alloy powder to obtain a diffusion source from the alloy powder; and a diffusion step of disposing the R1-T-B sintered magnet material and the diffusion source in a processing vessel, heating the R1-T-B sintered magnet material and the diffusion source to a temperature not higher than the sintering temperature of the R1-T-B sintered magnet material, and diffusing at least one of Dy and Tb contained in the diffusion source from the surface of the R1-T-B sintered magnet material into the inside, wherein the alloy is an alloy produced by a melt-spinning method.

In another exemplary embodiment, a method for producing an R-T-B sintered magnet according to the present disclosure includes: a step for preparing a R1-T-B sintered magnet material (R1 is a rare earth element, and T is Fe or Fe and Co); a step of preparing an alloy containing at least one rare earth element R2 that necessarily includes Dy and Tb and occupies 40 mass% or more of the entire alloy; a step of heat-treating the alloy at a temperature not lower than 230 ℃ but not higher than the melting point of the alloy, and pulverizing the heat-treated alloy to obtain a diffusion source; and a diffusion step of disposing the R1-T-B sintered magnet material and the diffusion source in a process vessel, heating the R1-T-B sintered magnet material and the diffusion source to a temperature not higher than the sintering temperature of the R1-T-B sintered magnet material, and diffusing at least one of Dy and Tb contained in the diffusion source from the surface of the R1-T-B sintered magnet material into the interior, wherein the alloy is an alloy produced by strip casting (strip cast).

In another exemplary embodiment, a method for producing an R-T-B sintered magnet according to the present disclosure includes: a step for preparing a R1-T-B sintered magnet material (R1 is a rare earth element, and T is Fe or Fe and Co); a step of crushing an alloy containing at least one rare earth element R2 that necessarily includes Dy and Tb and occupies 40 mass% or more of the entire alloy to prepare an alloy powder; a step of heat-treating the alloy powder at a temperature which is 230 ℃ or higher and lower than the melting point of the alloy powder to obtain a diffusion source from the alloy powder; and a diffusion step of disposing the R1-T-B sintered magnet material and the diffusion source in a processing vessel, heating the R1-T-B sintered magnet material and the diffusion source to a temperature not higher than the sintering temperature of the R1-T-B sintered magnet material, and diffusing at least one of Dy and Tb contained in the diffusion source from the surface of the R1-T-B sintered magnet material into the interior, wherein the alloy is an alloy produced by a strip casting method.

In one embodiment, the alloy is an RHRLM1M2 alloy (RH is one or more selected from Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and necessarily includes at least one of Tb and Dy, RL is one or more selected from La, Ce, Pr, Nd, Pm, Sm, and Eu, and necessarily includes at least one of Pr and Nd), M1 and M2 are one or more selected from Cu, Fe, Ga, Co, Ni, and Al, and may be M1 ═ M2).

In one embodiment, the alloy is an RHM1M2 alloy (RH is one or more selected from Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and necessarily includes at least one of Tb and Dy), M1 and M2 are one or more selected from Cu, Fe, Ga, Co, Ni, and Al, and may be M1 ═ M2).

In an exemplary embodiment, the diffusion source of the present disclosure is an alloy powder containing at least 40 mass% or more of R2, which is a rare earth element that necessarily includes at least one of Dy and Tb, in the entire body, wherein the alloy powder is composed of particles of an intermetallic compound having an average crystal grain diameter of more than 3 μm, and the cross section of the particles is in the form of flakes.

In one embodiment, the alloy powder is a RHRLM1M2 alloy (RH is one or more selected from Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and necessarily includes at least one of Tb and Dy, RL is one or more selected from La, Ce, Pr, Nd, Pm, Sm, and Eu, and necessarily includes at least one of Pr and Nd), M1 and M2 are one or more selected from Cu, Fe, Ga, Co, Ni, and Al, and may be M1 ═ M2).

In one embodiment, the alloy powder is a powder of an RHM1M2 alloy (RH is one or more selected from Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and necessarily includes at least one of Tb and Dy), and M1 and M2 are one or more selected from Cu, Fe, Ga, Co, Ni, and Al, and may be M1 ═ M2).

ADVANTAGEOUS EFFECTS OF INVENTION

According to the embodiment of the present disclosure, since the structure of the diffusion source containing at least one of Dy and Tb is modified, it is possible to improve the H content of the R-T-B sintered magnet while suppressing fluctuations in magnetic characteristics_cJ。

Drawings

Fig. 1A is a schematic sectional view showing a part of an R1-T-B-based sintered magnet raw material prepared in an embodiment of the present disclosure.

Fig. 1B is a schematic sectional view showing a part of an R1-T-B-based sintered magnet raw material in a state of being in contact with a diffusion source in the embodiment of the present disclosure.

Detailed Description

In the present specification, the rare earth element is at least one element selected from scandium (Sc), yttrium (Y), and lanthanoid elements. Here, the lanthanoid element is a generic name of 15 elements from lanthanum to lutetium. R1 and R are rare earth elements, and R2 is a rare earth element that necessarily includes at least one of Dy and Tb.

An exemplary embodiment of a method for manufacturing an R-T-B sintered magnet according to the present disclosure includes:

1. a step for preparing a R1-T-B sintered magnet material (R1 is a rare earth element, and T is Fe or Fe and Co);

2. a step of preparing an alloy containing at least one rare earth element R2 that necessarily includes Dy and Tb and occupies 40 mass% or more of the entire alloy;

3. a step of heat-treating the alloy at a temperature not lower than 270 ℃ and not higher than the melting point of the alloy, and pulverizing the heat-treated alloy to obtain a diffusion source;

4. and a diffusion step of disposing the R1-T-B sintered magnet material and the diffusion source in a processing vessel, heating the R1-T-B sintered magnet material and the diffusion source to a temperature not higher than the sintering temperature of the R1-T-B sintered magnet material, and diffusing at least one of Dy and Tb contained in the diffusion source from the surface of the R1-T-B sintered magnet material into the inside.

In this embodiment, the alloy is an alloy produced by a melt-spinning method.

Further, another exemplary embodiment of the R-T-B sintered magnet according to the present disclosure includes:

1'. preparing a R1-T-B sintered magnet material (R1 is a rare earth element, and T is Fe or Fe and Co);

a step of pulverizing an alloy containing at least one rare earth element R2 including Dy and Tb in an amount of 40 mass% or more of the entire alloy to prepare an alloy powder;

3' heat-treating the alloy at a temperature of 270 ℃ or higher and a temperature of not higher than the melting point of the alloy powder to obtain a diffusion source from the alloy powder;

and a diffusion step of disposing the R1-T-B sintered magnet material and the diffusion source in a processing vessel, heating the R1-T-B sintered magnet material and the diffusion source to a temperature not higher than the sintering temperature of the R1-T-B sintered magnet material, and diffusing at least one of Dy and Tb contained in the diffusion source from the surface of the R1-T-B sintered magnet material into the inside.

In this embodiment, the alloy is also an alloy produced by a melt-spinning method.

Another exemplary embodiment of a method for manufacturing an R-T-B sintered magnet according to the present disclosure includes:

3. a step of heat-treating the alloy at a temperature not lower than 230 ℃ but not higher than the melting point of the alloy, and pulverizing the heat-treated alloy to obtain a diffusion source;

In this embodiment, the alloy is an alloy produced by a strip casting method.

3' a step of heat-treating the alloy powder at a temperature not lower than 230 ℃ but not higher than the melting point of the alloy powder to obtain a diffusion source from the alloy powder;

and 4' a diffusion step of disposing the R1-T-B sintered magnet material and the diffusion source in a process container, heating the R1-T-B sintered magnet material and the diffusion source to a temperature not higher than the sintering temperature of the R1-T-B sintered magnet material, and diffusing at least one of Dy and Tb contained in the diffusion source from the surface of the R1-T-B sintered magnet material into the interior.

In this embodiment, the alloy is an alloy produced by a strip casting method.

As described above, the alloy powder constituting the diffusion source by the heat treatment is composed of particles having an average crystal grain diameter exceeding 3 μm. Thus, the preferable range of the heat treatment differs depending on the alloy obtained by the melt-spinning method and the strip casting method. In addition, in order to obtain a diffusion source composed of particles of the intermetallic compound having an average crystal grain diameter of more than 3 μm, a method other than the above-described heat treatment may be used. For example, the intermetallic compound particles having an average crystal grain size of more than 3 μm can be obtained by adjusting the cooling conditions, holding temperature and holding time of the alloy obtained by the melt-spinning method and/or the strip casting method.

In the present disclosure, the above alloy is an alloy produced by a melt-spinning method or a strip casting method. Diffusion sources can be made from the alloy powder. In an exemplary embodiment of a diffusion source according to the present disclosure:

(1) the alloy powder contains at least one rare earth element R1 including Dy and Tb in an amount of 40 mass% or more of the whole.

(2) The alloy powder is composed of particles of an intermetallic compound having an average crystal grain diameter of more than 3 μm.

(3) The cross section of the particles is in the shape of flakes.

The diffusion source is composed of particles of an intermetallic compound having an average crystal grain diameter of more than 3 μm, and therefore, H in the R-T-B sintered magnet can be improved while suppressing fluctuations in characteristics_cJ。

In the present disclosure, the diffusion source is an alloy powder obtained by pulverizing an alloy produced by a melt-spinning method and/or a strip casting method. Therefore, the cross section of the particles of the powder constituting the diffusion source is in the form of flakes.

The differences between 1 to 4 and 1 'to 4' are only the differences between the case where the diffusion source is obtained by heat-treating the alloy and pulverizing the alloy after the heat treatment (1 to 4) and the case where the diffusion source is obtained by heat-treating the alloy powder obtained by pulverizing the alloy (1 'to 4'). Therefore, the descriptions 1 to 4 are omitted, and the descriptions of the above l 'to 4' are omitted.

Hereinafter, embodiments of the present disclosure will be described. In some cases, the detailed description may be omitted. For example, detailed descriptions of known matters and repetitive descriptions of substantially the same configuration may be omitted. This is to avoid unnecessarily obscuring the following description, as will be readily understood by those skilled in the art. The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the disclosure. The subject matter recited in the patent claims is not intended to be limited thereby.

1. Process for preparing R1-T-B sintered magnet material

An R1-T-B system sintered magnet material to be diffused with at least one of Dy and Tb was prepared (R1 is a rare earth element, and T is Fe or Fe and Co). As the R1-T-B sintered magnet material, a known magnet material can be used.

The R1-T-B sintered magnet material has the following composition, for example.

Rare earth element R1: 12 to 17 atom%

B (boron) may be partially substituted with C (carbon): 5 to 8 atom%

An additive element M (at least one selected from Al, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb and Bi): 0 to 5 atom%

T (transition metal element mainly containing Fe, which may contain Co) and inevitable impurities: the remaining part

Wherein the rare earth element R1 is mainly Nd and Pr, and may contain at least one of Dy and Tb.

The R1-T-B sintered magnet material having the above composition can be produced by any known production method. The R1-T-B sintered magnet material may be in a sintered state, or may be subjected to cutting or polishing. The shape and size of the R1-T-B sintered magnet material are arbitrary.

2. Step of preparing alloy

[ alloy ]

The alloy contains at least one rare earth element R2 that must include Dy and Tb in an amount of 40 mass% or more of the entire alloy. The alloy containing at least one rare earth element R2 including Dy and Tb in an amount of 40 mass% or more of the entire alloy may be, for example, rare earth element R2 composed of only at least one of Dy and Tb, or rare earth element R2 composed of at least one of Dy and Tb and at least one of Pr and Nd. In either case, the rare earth element R2 may be present in an amount of 40 mass% or more of the entire alloy. When the rare earth element R2 is less than 40 mass% of the whole, high H may not be obtained_cJ. Typical examples of alloys are the RHM1M2 alloy and the RHRLM1M2 alloy. Examples of these alloys are described below.

(RHM1M2 alloy)

Examples of the alloy include an RHM1M2 alloy (RH is one or more selected from Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and necessarily includes at least one of Tb and Dy), M1 and M2 are one or more selected from Cu, Fe, Ga, Co, Ni, and Al, and M1 ═ M2 may be used).

Typical examples of the RHM1M2 alloy are DyFe alloy, DyAl alloy, DyCu alloy, TbFe alloy, TbAl alloy, TbCu alloy, DyFeCu alloy, TbCuAl alloy, and the like.

(RHRLM1M2 alloy)

Another example of the alloy is RHRLM1M2 alloy (RH is one or more selected from Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and necessarily includes at least one of Tb and Dy, RL is one or more selected from La, Ce, Pr, Nd, Pm, Sm, and Eu, and necessarily includes at least one of Pr and Nd), M1 and M2 are one or more selected from Cu, Fe, Ga, Co, Ni, and Al, and may be M1 ═ M2). Typical examples of RHRLM1M2 alloys are TbNdCu alloy, DyNdCu alloy, TbNdFe alloy, DyNdFe alloy, TbNdCuAl alloy, DyNdCuAl alloy, TbNdCuCo alloy, DyNdCuCo alloy, TbNdCoGa alloy, DyNdCoGa alloy, TbNdPrCu alloy, DyNdPrCu alloy, TbNdPrFe alloy, DyNdPrFe alloy, and the like. The alloy is not limited to the above-mentioned RHM1M2 alloy and RHRLM1M2 alloy. Any alloy that necessarily includes at least one of Dy and Tb and contains the rare earth element R2 in an amount of 40 mass% or more of the entire alloy may contain other elements and impurities.

In the present disclosure, the alloy is made by a melt-spinning process or a strip casting process.

In the melt-spinning method, a molten alloy is sprayed onto the surface of a metal chill roll rotating at a high speed, and the molten alloy is brought into contact with the surface of the chill roll and rapidly solidified. In order to bring an appropriate amount of the alloy melt into contact with the surface of the cooling roll, the alloy melt is sprayed through a spout (hole) having an inner diameter narrowed to, for example, about 1 mm. The alloy formed is amorphous or microcrystalline. The alloy formed was a ribbon-like or scaly ribbon, and had a thickness of the order of 10 μm (less than 100 μm). However, in the present disclosure, as described later, the alloy is heat-treated to crystallize in an amorphous state and coarsen crystallites, thereby finally obtaining a texture suitable as a diffusion source.

The strip casting method is a method of continuously casting a thin-plate alloy by flowing a molten metal on a rotating roll and solidifying the molten metal into a thin-plate by quenching. The alloy formed is in the form of a thin plate having a thickness of the order of 100 μm (e.g., about 100 μm to 500 μm). In the present disclosure, as described later, the heat treatment is performed on the alloy to coarsen the crystallites, and finally, a microstructure suitable as a diffusion source is obtained.

When the molten alloy is rapidly solidified by melt-spinning or strip casting, it is difficult to strictly control the cooling rate. Therefore, the texture of each powder particle after the alloy is pulverized is liable to fluctuate. For example, the size of the tiny grains generated within the alloy varies greatly from particle to particle. Specifically, particles having an average crystal particle diameter of 1 μm or particles having an average crystal particle diameter of 3 μm were formed. If such fluctuations in the texture and average crystal grain size occur, the melting temperature of the phase constituting the grains and the rate of supply of Dy and Tb as diffusion sources fluctuate in the diffusion step described later. Such fluctuations eventually lead to fluctuations in the magnet characteristics.

In order to solve such a problem, the embodiment of the present disclosure performs the heat treatment described below.

3. Process for obtaining diffusion source

[ Heat treatment of alloy ]

In an embodiment of the present disclosure, an alloy obtained by the melt-spinning method is heat-treated at a temperature not lower than 270 ℃ and not higher than the melting point of the alloy. On the other hand, the alloy obtained by the strip casting method is heat-treated at a temperature not lower than the melting point of the alloy by 230 ℃ and not higher than the melting point.

Thereby, the crystallinity of the particles constituting the alloy is modified. Further, by pulverizing the alloy (alloy after heat treatment), a diffusion source having more excellent uniformity can be obtained, and by using the diffusion source, fluctuation of magnetic properties in the diffusion step can be suppressed. The alloy may be pulverized by a known pulverization method such as pin mill pulverization, and the size of the pulverized powder particles may be 300 μm or less (preferably 200 μm or less). The heat treatment time may be, for example, 30 minutes to 10 hours. In such a diffusion source, the average crystal grain size of the intermetallic compound phase exceeds 3 μm. The average crystal grain size of the intermetallic compound phase in the diffusion source is preferably 3.5 μm or more and 20 μm or less. The intermetallic compound phase refers to the entire crystal grains of the intermetallic compound in the powder grains constituting the diffusion source. When the intermetallic compound in the powder particles constituting the diffusion source is plural, it means the whole crystal grains of the intermetallic compound having the largest content.

When the heat treatment temperature of the alloy powder is lower than 270 ℃ lower than the melting point of the alloy powder, the crystallinity of the powder particles constituting the alloy powder may not be improved because the temperature is too low, and when the temperature exceeds the melting point, the powders may fuse with each other and the diffusion treatment may not be efficiently performed.

The heat treatment is preferably performed by adjusting the atmosphere in the furnace so that the oxygen content in the diffusion source after the heat treatment is 0.5 mass% or more and 4.0 mass% or less. By intentionally oxidizing the entire surface of the alloy, the fluctuation in the characteristics of each particle due to the difference in the contact time between the powder particles and the atmosphere, the humidity, and the like can be reduced, and the fluctuation in the magnetic characteristics in the diffusion step can be further reduced. In addition, the possibility of ignition due to contact with oxygen in the atmosphere can be reduced. Therefore, quality control of the diffusion source becomes easy.

In an embodiment, the diffusion source is in the form of a powder. The particle size of the diffusion source in the powder state can be adjusted by sieving. Further, when the powder to be removed by sieving is 10% by mass or less, the influence is small, and therefore, it may be used without sieving.

The diffusion source in the form of powder may be granulated together with a binder as necessary. [ diffusion aid ]

The diffusion source obtained by subjecting the alloy to the above-described heat treatment and further pulverizing the above-described alloy may further contain an alloy powder that functions as a diffusion aid. An example of such an alloy is the RLM1M2 alloy. RL is one or more selected from La, Ce, Pr, Nd, Pm, Sm, Eu, and at least one of Pr and Nd, M1 and M2 are one or more selected from Cu, Fe, Ga, Co, Ni, and Al, and may be M1 ═ M2. Typical examples of the RLM1M2 alloy include an NdCu alloy, an NdFe alloy, an NdCuAl alloy, an NdCuCo alloy, an NdCoGa alloy, an NdPrCu alloy, and an NdPrFe alloy. These alloy powders may be used in combination with the alloy powders described above. Multiple RLM1M2 alloy powders may be mixed into an alloy powder.

The method for producing the RLM1M2 alloy powder is not particularly limited. When the cast metal is produced by a quenching method or cast metal method, it is preferable to use M1 ≠ M2, and for example, a ternary or higher alloy such as NdCuAl alloy, NdCuCo alloy, and NdCoGa alloy is used in order to improve the grindability. The particle size of the RLM1M2 alloy powder is, for example, 200 μ M or less, and the particle size of the small alloy powder is about 10 μ M.

As described above, the diffusion source in the embodiment of the present disclosure may contain the alloy powder after the heat treatment as an essential constituent element, and may contain a powder made of another material.

When the diffusion source is used in combination with the RLM1M2 alloy powder, it may be difficult to mix these powders uniformly with each other. The reason for this is that the alloy powder generally has a relatively small particle size compared to the RLM1M2 alloy powder. Therefore, it is preferable to granulate the RLM1M2 alloy powder, the alloy powder, and the binder. By using such granulated particles, there is an advantage that the mixing ratio of the RLM1M2 alloy powder and the alloy powder can be made uniform throughout the entire powder. In addition, it can be uniformly present on the surface of the magnet.

As the binder, a binder that does not cause adhesion or aggregation when the mixed solvent is dried or removed and that keeps smooth fluidity of powder particles constituting a diffusion source is preferable. Examples of the binder include PVA (polyvinyl alcohol). An aqueous solvent such as water or an organic solvent such as NMP (N-methylpyrrolidone) may be suitably used for mixing. The solvent is evaporated and removed by the granulation process described later.

The method of granulating with the binder may be any method. Examples thereof include a tumbling granulation method, a fluidized bed granulation method, a vibration granulation method, a high-speed air impact method (hyperbiliza), a method in which a powder and a binder are mixed, solidified, and then crushed.

In the embodiment of the present disclosure, it is not necessarily excluded that the powder other than the above-described powder (third powder) is present on the surface of the R1-T-B-based sintered magnet raw material, but it is necessary to take care that the third powder does not hinder diffusion of at least one of Dy and Tb in the diffusion source into the interior of the R1-T-B-based sintered magnet raw material. The mass ratio of "the alloy containing at least one of Dy and Tb" in the entire powder present on the surface of the R1-T-B-based sintered magnet raw material is preferably 70% or more.

Diffusion step of at least one of Dy and Tb

In order to heat the R1-T-B sintered magnet material and the diffusion source to a temperature not higher than the sintering temperature of the R1-T-B sintered magnet material, first, the R1-T-B sintered magnet material and the diffusion source are disposed in a processing vessel. In this case, it is preferable that the R1-T-B sintered magnet material and the diffusion source are contacted in the processing container.

[ arrangement ]

The R1-T-B sintered magnet material may be brought into contact with the diffusion source in any manner. For example, there may be mentioned: a method of attaching a powdery diffusion source to the R1-T-B-based sintered magnet raw material coated with the binder by using a flow-dipping method; a method of immersing a R1-T-B sintered magnet material in a processing vessel containing a powdery diffusion source; and a method of spraying a powdery diffusion source on the R1-T-B sintered magnet material. Further, the treatment container containing the diffusion source may be vibrated, shaken, or rotated, or the powder of the diffusion source may be made to flow in the treatment container.

Fig. 1A is a schematic cross-sectional view showing a part of an R1-T-B-based sintered magnet raw material 100 that can be used in the method for producing an R-T-B-based sintered magnet according to the present disclosure. In the figure, the upper surface 100a and side surfaces 100B and 100c of the R1-T-B sintered magnet material 100 are shown. The shape and size of the R1-T-B sintered magnet material used in the production method of the present disclosure are not limited to the shape and size of the illustrated R1-T-B sintered magnet material 100. The upper surface 100a and the side surfaces 100B and 100c of the illustrated R1-T-B sintered magnet material 100 are flat, but the surface of the R1-T-B sintered magnet material 100 may have irregularities or height differences, or may be curved.

Fig. 1B is a schematic cross-sectional view of a part of the R1-T-B-based sintered magnet raw material 100 showing a state in which the powder particles 30 constituting the diffusion source are located on the surface. The powder particles 30 constituting the diffusion source on the surface of the R1-T-B based sintered magnet material 100 may be adhered to the surface of the R1-T-B based sintered magnet material 100 via an unillustrated adhesive layer. Such an adhesive layer can be formed by, for example, coating the surface of the R1-T-B sintered magnet material 100. By using the adhesive layer, the powder of the diffusion source can be easily attached to a plurality of regions (for example, the upper surface 100a and the side surface 100B) having different normal directions by one coating step without changing the orientation of the R1-T-B sintered magnet material 100.

Examples of the binder that can be used include PVA (polyvinyl alcohol), PVB (polyvinyl butyral), PVP (polyvinyl pyrrolidone), and the like. When the binder is an aqueous binder, the R1-T-B sintered magnet material may be preheated before coating. The purpose of preheating is to remove excess solvent, control adhesion, and make the adhesive adhere uniformly. The heating temperature is preferably 60 to 100 ℃. In the case of an organic solvent-based adhesive having high volatility, this step can be omitted.

The method of applying the binder to the surface of the R1-T-B sintered magnet material may be any method. Specific examples of the coating include a spray coating method, a dipping method, and coating with a dispenser.

In a preferred embodiment, a binder is applied to the entire surface (entire surface) of the R1-T-B sintered magnet material. Instead of coating the entire surface of the R1-T-B sintered magnet material, a part of the material may be adhered. In particular, when the R1-T-B sintered magnet material has a small thickness (e.g., about 2 mm), there is a case where at least one of Dy and Tb can be diffused into the entire magnet by attaching the powder of the diffusion source only to the one surface having the largest area among the surfaces of the R1-T-B sintered magnet material, thereby increasing H_cJ。

The powder particles constituting the diffusion source in contact with the surface of the R1-T-B-based sintered magnet material 100 have a structure with excellent uniformity as described above. In addition, in one embodiment, the entire surface of the alloy particles is oxidized, and therefore, the possibility of ignition due to contact of the powder particles with oxygen in the atmosphere is reduced, and fluctuation in characteristics due to contact with the atmosphere is also reduced. Therefore, at least one of Dy and Tb contained in the diffusion source can be efficiently diffused from the surface of the R1-T-B sintered magnet material into the interior without waste when heating for diffusion described later is performed.

The amount of at least one of Dy and Tb contained in the diffusion source on the surface of the magnet may be set to be, for example, in the range of 0.5 to 3.0% by mass relative to the R1-T-B sintered magnet raw material. In order to obtain higher H_cJThe content of the carbon black is set to be in the range of 0.7 to 2.0%.

Further, the amount of at least one of Dy and Tb contained in the diffusion source depends not only on the concentration of Dy and Tb in the powder particles but also on the particle size of the powder particles constituting the diffusion source. Therefore, the amounts of Dy and Tb diffused by adjusting the particle size of the powder particles constituting the diffusion source by making the concentrations of Dy and Tb constant can also be adjusted.

[ Heat treatment ]

The temperature for the heat treatment for diffusion is not higher than the sintering temperature of the R1-T-B sintered magnet material (specifically, not higher than 1000 ℃). When the diffusion source contains a powder of an RLM1M2 alloy or the like, the temperature is higher than the melting point of the alloy, for example, 500 ℃. The heat treatment time is, for example, 10 minutes to 72 hours. After the heat treatment, the heat treatment may be further performed at 400 to 700 ℃ for 10 minutes to 72 hours, if necessary.

By such heat treatment, at least one of Dy and Tb contained in the diffusion source can be diffused from the surface to the interior of the R1-T-B sintered magnet raw material.

The production method may be the same as 1 to 4 except that the alloy powder obtained by the melt spinning method or the strip casting method is pulverized by a known method such as pulverization by a pin mill, etc. to prepare an alloy powder, and the alloy powder is heat-treated at a temperature of 230 ℃ or higher and not higher than the melting point of the alloy powder, as described above, although the description of 1 'to 4' is omitted.

Examples

(Experimental example 1)

First, an R1-T-B-based sintered magnet material having a composition ratio of Nd 23.4, Pr 6.2, B1.0, Al 0.4, Cu 0.1, Co 1.5, and the balance Fe (mass%) was produced by a known method. The dimensions of the R1-T-B sintered magnet material were 5.0mm in thickness, 7.5mm in width and 35mm in length.

Next, alloys were prepared by a melt-spinning method so as to have compositions substantially shown in table 1. Specifically, in a chamber formed in an argon atmosphere of 80kPa, the raw material was dissolved by high frequency in a quartz nozzle having a nozzle diameter of 0.8mm, and then the melt was ejected onto a Cu roll by applying a back pressure of 100 kPa. The circumferential speed of the Cu roller is in the range of 10 to 40m/s depending on the composition. Next, the alloy was heat-treated under the conditions (temperature and time) shown in table 1 (however, No.1 was not heat-treated), and the heat-treated alloy was pulverized by a pin mill to obtain diffusion sources (nos. 1 to 13). The particle size of the diffusion source (alloy powder) was sieved and found to be 200 μm or less (confirmed by sieving). The compositions of the alloy powders in table 1 were measured using high-frequency inductively coupled plasma emission spectrometry (ICP-OES).

The average crystal grain size of the intermetallic compound phase in the obtained diffusion source was measured by the following method.

First, a cross section of powder particles constituting a diffusion source is observed with a Scanning Electron Microscope (SEM), phases are identified from contrast, and the composition of each phase is analyzed using energy dispersive X-ray spectroscopy (EDX) to determine an intermetallic compound phase. Next, the intermetallic compound phase having the highest area ratio was set as the intermetallic compound phase having the highest content by using image analysis software (Scandium), and the crystal grain size of the intermetallic compound phase was determined. Specifically, the number of crystal grains and the total area of crystal grains in the intermetallic compound phase were obtained by image analysis software (Scandium), and the average area was obtained by dividing the obtained total area of crystal grains by the number of crystal grains. Next, the crystal grain diameter D is determined from the obtained average area by formula 1.

[ formula 1]

Wherein D is a crystal grain diameter and S is an average area.

These operations were carried out 5 times (5 powder particles were investigated) to obtain the average value thereof, thereby obtaining the average crystal grain size of the intermetallic compound phase in the diffusion source. The results are shown in the average crystal grain size in table 1. In addition, since No.1 did not heat treat the diffusion source, the crystal grain size of the intermetallic compound phase was too small (fine crystal grains of 1 μm or less), and it was not measured.

Next, a binder is applied to the R1-T-B sintered magnet material. The coating method comprises the following steps: the R1-T-B sintered magnet material was heated to 60 ℃ on a hot plate, and then the entire surface of the R1-T-B sintered magnet material was coated with a binder by a spray coating method. PVP (polyvinylpyrrolidone) was used as a binder.

Next, the diffusion sources of Nos. 1 to 13 in Table 1 were attached to the R1-T-B sintered magnet material coated with the binder. In the R1-T-B sintered magnet material to which the diffusion sources were attached, 50 diffusion sources were prepared for each type (Nos. 1 to 13). The adhering method comprises the following steps: a diffusion source (alloy powder) is spread in a container, and after the temperature of the R1-T-B sintered magnet material coated with a binder is lowered to normal temperature, the diffusion source is attached to the entire surface of the R1-T-B sintered magnet material in the container.

Next, the R1-T-B sintered magnet material and the diffusion source were placed in a processing vessel and heated at 900 ℃ (sintering temperature or lower) for 8 hours, thereby performing a diffusion step of diffusing at least one of Dy and Tb contained in the diffusion source from the surface to the inside of the R1-T-B sintered magnet material. A cube having a thickness of 4.5mm, a width of 7.0mm and a length of 7.0mm was cut out from the central portion of the R-T-B sintered magnet after diffusion, the coercive force was measured by a B-H meter for each of 10 diffusion source types (Nos. 1 to 13), and the value obtained by subtracting the minimum value of the coercive force from the maximum value of the coercive force obtained was used as the magnetic property fluctuation (. DELTA.H)_cJ) And (4) obtaining.

Will be Δ H_cJThe values of (A) are shown in Table 1.

[ Table 1]

As shown in Table 1, the inventive examples (Nos. 2 to 5, and 7 to 13) had Δ H values in comparison with those of No.1 (comparative example) in which the alloy powder was not heat-treated and No.6 (comparative example) in which the heat treatment temperature was outside the range of the present disclosure_cJThe magnetic properties are about half of the values, and fluctuation of the magnetic properties in the diffusion step is suppressed.

(Experimental example 2)

An experimental example was carried out in the same manner as in experimental example 1 except that a strip casting method was used instead of the melt-spinning method to produce an alloy.

Specifically, alloys were prepared by strip casting so as to have compositions substantially shown in table 2. Next, the alloy was heat-treated under the conditions (temperature and time) shown in table 2 (however, No.14 was not heat-treated), and the alloy needles after the heat treatment were ground by a mill, thereby obtaining diffusion sources (nos. 14 to 25). The particle size of the diffusion source (alloy powder) was 200 μm or less (confirmed by sieving). The compositions of the alloy powders in table 2 were measured using high-frequency inductively coupled plasma emission spectrometry (ICP-OES).

[ Table 2]

As shown in Table 2, the inventive examples (Nos. 15 to 18, 20 to 25) had Δ H values in comparison with those of No.14 (comparative example) in which the alloy powder was not heat-treated and No.19 (comparative example) in which the heat treatment temperature was outside the range of the present disclosure_cJThe magnetic properties are all half or less, and fluctuation in magnetic properties in the diffusion step is suppressed.

Industrial applicability of the invention

Embodiments of the present disclosure can improve H of R-T-B sintered magnets with less Dy and Tb_cJTherefore, it can be used for producing a rare earth sintered magnet requiring a high coercive force. The present disclosure can also be applied to a rare earth sintered magnet containing a metal element other than the heavy rare earth element RHAnd is diffused from the surface.

Description of the symbols

30 powder particles constituting a diffusion source

100R 1-T-B sintered magnet material

Upper surface of 100a R1-T-B series sintered magnet raw material

Side surface of 100B R1-T-B sintered magnet material

Side surface of 100c R1-T-B sintered magnet material

Claims

1. A method for producing an R-T-B sintered magnet, comprising:

preparing a R1-T-B sintered magnet material, wherein R1 is a rare earth element, and T is Fe or Fe and Co;

a step of preparing an alloy containing at least one rare earth element R2 that necessarily includes Dy and Tb and occupies 40 mass% or more of the entire alloy;

a step of heat-treating the alloy at a temperature not lower than 270 ℃ and not higher than the melting point of the alloy, and pulverizing the heat-treated alloy to obtain a diffusion source; and

a diffusion step of disposing the R1-T-B sintered magnet material and the diffusion source in a processing vessel, heating the R1-T-B sintered magnet material and the diffusion source to a temperature not higher than the sintering temperature of the R1-T-B sintered magnet material, and diffusing at least one of Dy and Tb contained in the diffusion source from the surface of the R1-T-B sintered magnet material into the inside,

the alloy is prepared by a melt-state spinning method.

2. A method for producing an R-T-B sintered magnet, comprising:

a step of crushing an alloy containing at least one rare earth element R2 that necessarily includes Dy and Tb and occupies 40 mass% or more of the entire alloy to prepare an alloy powder;

a step of heat-treating the alloy powder at a temperature not lower than 270 ℃ and not higher than the melting point of the alloy powder to obtain a diffusion source from the alloy powder; and

the alloy is prepared by a melt-state spinning method.

3. The method of manufacturing an R-T-B sintered magnet according to claim 1 or 2, wherein:

the alloy is RHRLM1M2 alloy, wherein RH is more than one selected from Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and certainly comprises at least one of Tb and Dy, RL is more than one selected from La, Ce, Pr, Nd, Pm, Sm and Eu, and certainly comprises at least one of Pr and Nd, M1 and M2 are more than one selected from Cu, Fe, Ga, Co, Ni and Al, and the condition that M1 is M2 or M1 is not M2 is satisfied.

4. The method of manufacturing an R-T-B sintered magnet according to claim 1 or 2, wherein:

the alloy is an RHM1M2 alloy, wherein RH is more than one selected from Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and at least one selected from Tb and Dy is necessarily included, M1 and M2 are more than one selected from Cu, Fe, Ga, Co, Ni and Al, and M1 is equal to M2 or M1 is equal to M2.

5. A method for producing an R-T-B sintered magnet, comprising:

a step of heat-treating the alloy at a temperature that is 230 ℃ or higher and below the melting point of the alloy, and pulverizing the heat-treated alloy to obtain a diffusion source; and

the alloy is an alloy produced by a strip casting method.

6. A method for producing an R-T-B sintered magnet, comprising:

a step of heat-treating the alloy powder at a temperature which is 230 ℃ or higher and lower than the melting point of the alloy powder to obtain a diffusion source from the alloy powder; and

the alloy is an alloy produced by a strip casting method.

7. The method of manufacturing an R-T-B sintered magnet according to claim 5 or 6, wherein:

8. The method of manufacturing an R-T-B sintered magnet according to claim 5 or 6, wherein:

9. A diffusion source, characterized by:

which is used for diffusion to R1-T-B system sintered magnet raw material, wherein R1 is rare earth element, T is Fe or Fe and Co,

the diffusion source is an alloy powder containing at least one rare earth element R2 necessarily including Dy and Tb in an amount of 40 mass% or more of the entire powder,

the alloy powder is composed of particles of an intermetallic compound having an average crystal grain diameter of more than 3 μm,

the cross-section of the particles is in the shape of flakes,

the diffusion source is obtained by the following steps:

preparing an alloy containing at least one rare earth element R2 including Dy and Tb in an amount of 40 mass% or more of the entire alloy, heat-treating the alloy at a temperature of 270 ℃ or more and not more than the melting point of the alloy, and pulverizing the heat-treated alloy to obtain a diffusion source, wherein the oxygen content in the heat-treated diffusion source is 0.5 mass% or more and 4.0 mass% or less,

the alloy is prepared by a melt-state spinning method.

10. A diffusion source, characterized by:

the cross-section of the particles is in the shape of flakes,

the diffusion source is obtained by the following steps:

preparing an alloy containing R2, which is a rare earth element necessarily including at least one of Dy and Tb, in an amount of 40 mass% or more of the entire alloy, heat-treating the alloy at a temperature 230 ℃ or more and not more than the melting point of the alloy, and pulverizing the heat-treated alloy to obtain a diffusion source, wherein the oxygen content in the heat-treated diffusion source is 0.5 mass% or more and 4.0 mass% or less,

the alloy is an alloy produced by a strip casting method.

11. The diffusion source of claim 9 or 10, wherein:

the alloy powder is RHRLM1M2 alloy powder, wherein RH is more than one selected from Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and certainly comprises at least one of Tb and Dy, RL is more than one selected from La, Ce, Pr, Nd, Pm, Sm and Eu, and certainly comprises at least one of Pr and Nd, M1 and M2 are more than one selected from Cu, Fe, Ga, Co, Ni and Al, and the condition that M1 is M2 or M1 is not M2 is satisfied.

12. The diffusion source of claim 9 or 10, wherein:

the alloy powder is RHM1M2 alloy powder, wherein RH is more than one selected from Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and necessarily comprises at least one of Tb and Dy, M1 and M2 are more than one selected from Cu, Fe, Ga, Co, Ni and Al, and M1 is equal to M2 or M1 is not equal to M2.